Thermally-protective intumescent coating system and method

ABSTRACT

An intumescent coating system and method therefor is disclosed for thermally protecting a substrate having a surface exposed to fire conditions. The coating system of the present invention is provided as having a having a first film layer which forms a rigid carbonific char foam having toughness and rigidity, and a second film layer which forms an insulative carbonific char foam having insulation properties. The two foam components may be separately provided in a laminate-type arrangement as, respectively, an inner coating layer coated and cured on the surface of the substrate to form an inner film layer, and an outer coating layer coated and cured on the inner film layer to form an outer film layer. In providing two foam components, one protecting the substrate from breakthrough and direct exposure to the fire conditions, and the other insulating the substrate to protect it from conductive, radiant, and/or convective heating by the fire conditions, the present invention affords a capability to offer flame retardancy at film thicknesses of 1.27 mm (50 mils) or less.

The Government of the United States has rights in this invention undercontract No. A4124-900.

This application is a continuation application that claims priority fromcopending application Ser. No. 08/776,548, filed May 19, 1997, pending,that is a national application of PCT application PCT/US95/09761, now WO96/03854, filed Aug. 1, 1995, that claims priority from application Ser.No. 08/284,362, filed Aug. 2, 1994 (now U.S. Pat. No. 5,487,946).

BACKGROUND OF THE INVENTION

The present invention relates to intumescent coatings, such as thoseused as paints and the like, and to methods utilizing such coatings forfire retardance. For structures fabricated from polymeric materials andthe like, flame spread and thermal decomposition generally isaccelerated to the point that normal fire fighting response times areinadequate to prevent significant combustion of the structure.Accordingly, intumescent coatings have been employed as paints to form aprotective layer on the surface of such structures. As the name implies,intumescent coatings bubble when exposed to flames and produce aninsulative layer of char and char foam.

The relatively low tendency for elemental carbon to oxidize has led toits incorporation into intumescent coatings. In this regard,highly-flammable substrates can be thermally-protected by application ofa surface coating having ingredients catalyzed to be pyrolized into acarbonific char. Thus, the coating is converted from an oxidizablecomposition into elemental carbon. Broadly, such coatings comprise apolyhydric organic compound, an acid forming catalyst, and a blowingagent which intumesces the carbonific char formed from theacid-catalyzed pyrolysis of the polyhydric compound into a carbonificchar foam having a relatively low thermal conductivity.

On its own, a pure carbon foam would not be expected to provide optimalthermal insulation. Consequently, the carbon foam often is supplementedwith inorganic additives. Some inorganics, e.g., titanium dioxide andzinc oxide, provide nucleating sites for gas formation, resulting infine cell, low density foam. Inasmuch as heat conduction through a gascan be several orders of magnitude lower than through a solid, a lowdensity foam provides insulation improved over a higher density foam,especially when coated on a heat-conducting substrate such as a metal ora carbon-fiber composite.

Additionally, several inorganics, including zirconium salts, borates,phosphates, and titanium dioxide, can contribute to the formation of arefractory layer over the top of the foam layer. The refractory layeradvantageously provides an inert, highly infrared reflective layer,which can contribute significantly to the insulative properties of thefoam. The infrared reflectance of the char also may be improved by theaddition of inorganics having low emissivities such as titanium dioxide,zirconium dioxide, phosphate and antimonate glass. Other inorganics suchas silica microballoons and silicone resins may be added to decreaseheat conduction through the foam.

To form intumescent coatings having good integrity and offeringresistance to high humidity, water-insoluble intumescent or char-formingagents, including selective salts of nitro aromatic amine compounds suchas 4,4'-dinitrosulfanilimide, have been blended with epoxy-polysulfideor epoxy-chlorosulfonated polyethylene binder systems. Although suchformulations are efficient intumescents, their efficiency is notoptimized because the nitro aromatic intumescent species produces anexothermic char-forming reaction. To counter this exothermic effect,ablatives and endothermic fillers, including zinc borate and hydratedendothermic fillers such as aluminum hydroxide pigments, are beneficial.

The intumescent coatings heretofore known in the art have been usedsuccessfully to effectively reduce flame spread and to protectsubstrates from thermally-induced mechanical/chemical decomposition.Although these coatings have demonstrated significant fire retardantproperties, they generally must be used at thicknesses, e.g., ≧5.08 mm(≧200 mils), which precludes their use in applications where weightrequirements are a consideration. Moreover, conventional coatings arenot formulated to withstand exposure to the severe environments commonin marine applications and the like, and often have ingredients whichleach out after extended immersion in seawater. For certainapplications, the intumescent reaction temperature of conventionalformulations may be at or near the service temperature. Accordingly,there has existed and remains a substantial need for intumescent coatingsystems which not only will afford the requisite thermal insulation atminimum coating thicknesses and at elevated service temperatures, butwhich also will retain an insulative capability even after exposure toharsh marine environments and the like.

BRIEF DESCRIPTION OF THE INVENTION

A first aspect of the invention includes a coating system for thermallyprotecting a substrate having a surface exposed to fire conditionscomprising: a first coating layer coated on the surface of the substrateand cured thereon to form a first film layer which layer is thermallydecomposable upon exposure to the fire conditions to form a firstcarbonific char which char intumesces to form a first rigid carbonificchar foam; and a second coating layer coated on the first film layer andcured thereon to form a second film layer which layer is thermallydecomposable upon exposure to the fire conditions to form a secondcarbonific char which char intumesces to form an insulative carbonificchar foam having a density about half the density of the first rigidcarbonific char foam, the first rigid carbonific char foam forming wherethe insulative carbonific char foam has broken through to expose thefirst film layer to the fire conditions. Typically the insulativecarbonific char foam has a density of between about 0.01 g/cm³ and lessthan about 0.5 g/cm³ and in some typical applications the firstcomponent is selected as having a density of between about 0.5 g/cm³ andless than about 1.0 g/cm³. In other typical embodiments the secondcoating layer comprises: a curable binder; a char promoter havinghydroxyl groups; a dehydrating agent which is thermally decomposable toform an acid catalyst, the char promoter dehydrating in the presence ofthe acid catalyst to form an intermediate species which intermediatespecies is thermally decomposable to form the second carbonific char;and a spumific which is thermally decomposable to release anonflammable, inert gas for foaming the second carbonific char into theinsulative carbonific char foam, the spumific having a decompositiontemperature higher than the decomposition temperatures of thedehydrating agent and the intermediate species. Typically the charpromoter is a polyhydric alcohol and may be selected from the groupconsisting of pentaerythritol, dipentaerythritol, and derivatives andmixtures thereof; the dehydrating agent is an acid precursor which isthermally decomposable to form the acid catalyst and the acid precursormay be selected from the group consisting of ammonium phosphate,ammonium polyphosphate, phosphites, organophosphite esters, andderivatives and mixtures thereof; the spumific is a dicyandiamide or anazodicarbonamide; or the binder is selected from the group consisting ofan epoxy, a polysulfide, a polysiloxane, a polysilarylene, and mixturesand derivatives thereof. Typically the first coating layer comprises anepoxy resin and a polysulfide.

In another typical embodiment the coating system of further comprises athird coating layer coated on the second film layer and cured thereon toform a third film layer which layer is thermally decomposable uponexposure to the fire conditions to form a third carbonific char whichchar intumesces to form a second rigid carbonific char foam having adensity about twice the density of the insulative carbonific char foam,the insulative carbonific char foam forming under the second rigidcarbonific char foam; and the third coating layer can typically comprisean epoxy resin and a polysulfide.

Alternatively, an embodiment includes a third coating layer formulatedas a blend of the first and the second coating layers, the third coatinglayer being coated on the second film layer and cured thereon to form athird film layer which layer is thermally decomposable upon exposure tothe fire conditions to form a third carbonific char which charintumesces to form a carbonific char foam blend having a first foamcomponent and a second foam component having a density of about half thedensity of the first foam component, the insulative carbonific char foamforming under the carbonific char foam blend. Typically the second foamcomponent has a density of between about 0.01 g/cm³ and less than about0.5 g/cm³.

A further typical embodiment of the invention includes a method forthermally protecting a substrate having a surface exposed to a fireconditions comprising the steps of: coating the surface of the substratewith a first coating layer, curing the first coating layer on thesurface of the substrate to form a first film layer which layer isthermally decomposable upon exposure to the fire conditions to form afirst carbonific char which char intumesces to form a first rigidcarbonific char foam; coating a second coating layer on the first filmlayer; and curing the second coating layer on the first coating layer toform a second film layer which layer is thermally decomposable uponexposure to the fire conditions to form a second carbonific char whichchar intumesces to form an insulative carbonific char foam having adensity about half the density height of the first rigid carbonific charfoam, the first rigid carbonific char foam forming where the insulativecarbonific char foam has broken through to expose the first film layerto the fire conditions. Typically the insulative carbonific char foamhas a density of between about 0.01 g/cm³ and less than about 0.5 g/cm³.In another embodiment thereof the second coating layer comprises: acurable binder, a char promoter having hydroxyl groups; a dehydratingagent which is thermally decomposable to form an acid catalyst, the charpromoter dehydrating in the presence of the acid catalyst to form anintermediate species which intermediate species is thermallydecomposable to form the second carbonific char; and a spumific which isthermally decomposable to release a nonflammable, inert gas for foamingthe second carbonific char into the insulative carbonific char foam, thespumific having a decomposition temperature higher than thedecomposition temperatures of the dehydrating agent and the intermediatespecies. Typically the char promoter is a polyhydric alcohol and thealcohol is selected from the group consisting of pentaerythritol,dipentaerythritol, and derivatives and mixtures thereof; the dehydratingagent is an acid precursor which is thermally decomposable to form theacid catalyst; the acid precursor is selected from the group consistingof ammonium phosphate, ammonium polyphosphate, phosphites,organophosphite esters, and derivatives and mixtures thereof; thespumific is a dicyandiamide or an azodicarbonamide; the binder isselected from the group consisting of an epoxy, a polysulfide, apolysiloxane, a polysilarylene, and mixtures and derivatives thereof;and/or the first layer comprises an epoxy resin and a polysulfide.

A further embodiment of the method includes the steps of: coating athird coating layer on the second film layer, and curing the thirdcoating layer on the second coating layer to form a third film layerwhich layer is thermally decomposable upon exposure to the fireconditions to form a third carbonific char which char intumesces to forma second rigid carbonific char foam having a density about twice thedensity of the insulative carbonific char foam, the insulativecarbonific char foam forming under the second rigid carbonific charfoam. The method typically includes an insulative carbonific char foamhaving a density of between about 0.01 g/cm³ and less than about 0.5g/cm³ ; the third coating layer comprising an epoxy resin and apolysulfide.

A yet further embodiment of the method includes the steps of coating athird coating layer on the second film layer, the third coating layerformulated as a blend of the first and the second coating layers; andcuring the third coating layer on the second coating layer to form athird film layer which layer is thermally decomposable upon exposure tothe fire conditions to form a third carbonific char which charintumesces to form a carbonific char foam blend having a first foamcomponent, and a second foam component having a density about half thefoam density of the first foam component, the insulative carbonific charfoam forming under the carbonific char foam blend.

A yet further embodiment of the invention typically includes a coatingcomposition for thermally protecting a substrate having a surfaceexposed to a fire conditions on which the composition is coated andcured to form a film layer, said composition comprising a blend of: afirst component which is curable to form a first portion of the filmlayer, the first portion being thermally decomposable to form a firstcarbonific char which char intumesces to form a rigid carbonific charfoam; and a second component which is curable to form a second portionof the film layer blended with the first portion, the second portionbeing thermally decomposable to form a second carbonific char which charintumesces to form an insulative carbonific char foam blended with therigid carbonific char and having a density about half the density of therigid carbonific char foam. Typically the insulative carbonific charfoam has a density of between about 0.01 g/cm³ and less than about 0.5g/cm³ and the rigid carbonific char foam is selected as having a densityof between about 0.5 g/cm³ and about 1.0 g/cm³. Typically the coatingcomposition is 75% by weight of the first component and 25% by weight ofthe second component.

In yet other embodiments the second component comprises: a curablebinder; a char promoter having hydroxyl groups; a dehydrating agentwhich is thermally decomposable to form an acid catalyst, the charpromoter dehydrating in the presence of the acid catalyst to form anintermediate species which intermediate species is thermallydecomposable to form the second carbonific char; and a spumific which isthermally decomposable to release a nonflammable, inert gas for foamingthe second carbonific char into the insulative carbonific char foam, thespumific having a decomposition temperature higher than thedecomposition temperatures of the dehydrating agent and the intermediatespecies. Typically the char promoter is a polyhydric alcohol; thealcohol is selected from the group consisting of pentaerythritol,dipentaerythritol, and derivatives and mixtures thereof; the dehydratingagent is an acid precursor which is thermally decomposable to form theacid catalyst; the acid precursor is selected from the group consistingof ammonium phosphate, ammonium polyphosphate, phosphites,organophosphite esters, and derivatives and mixtures thereof; thespumific is a dicyandiamide or an azodicarbonamide; the binder isselected from the group consisting of an epoxy, a polysulfide, apolysiloxane, a polysilarylene, and mixtures and derivatives thereof;and the first component can comprise an epoxy resin and a polysulfide.

Yet another embodiment includes a method for thermally protecting asubstrate having a surface exposed to a fire conditions comprising thesteps of: (a) coating the surface of the substrate with a coating layercomprising a blend of: (i) a first component which is curable to form afirst portion of a film layer, the first portion being thermallydecomposable to form a first carbonific char which char intumesces toform a rigid carbonific char foam; and (ii) a second component which iscurable to form a second portion of the film layer blended with thefirst portion, the second portion being thermally decomposable to form asecond carbonific char which char intumesces to form an insulativecarbonific char foam blended with the rigid carbonific char and having adensity about half the density of the rigid carbonific char foam, and(b) curing the coating layer on the surface of the substrate to form thefilm layer. Typically the insulative carbonific char foam has a densityof between about 0.01 g/cm³ and less than about 0.5 g/cm³ and the rigidcarbonific char foam of the first component is selected as having adensity of between about 0.5 g/cm³ and less than about 1.0 g/cm³. Inother embodiments the composition comprises 75% by weight of the firstcomponent and 25% by weight of the second component.

A yet further embodiment of the latter method includes a secondcomponent of the composition comprising: a curable binder; a charpromoter having hydroxyl groups; a dehydrating agent which is thermallydecomposable to form an acid catalyst, the char promoter dehydrating inthe presence of the acid catalyst to form an intermediate species whichintermediate species is thermally decomposable to form the secondcarbonific char; and a spumific which is thermally decomposable torelease a nonflammable, inert gas for foaming the second carbonific charinto the insulative carbonific char foam, the spumific having adecomposition temperature higher than the decomposition temperatures ofthe dehydrating agent and the intermediate species. Typically the charpromoter is a polyhydric alcohol; the alcohol is selected from the groupconsisting of pentaerythritol, dipentaerythritol, and derivatives andmixtures thereof; the dehydrating agent is an acid precursor which isthermally decomposable to form the acid catalyst; the acid precursor isselected from the group consisting of ammonium phosphate, ammoniumpolyphosphate, phosphites, organophosphite esters, and derivatives andmixtures thereof; the spumific is a dicyandiamide or anazodicarbonamide; the binder is selected from the group consisting of anepoxy, a polysulfide, a polysiloxane, a polysilarylene, and mixtures andderivatives thereof; and/or the first component of the compositioncomprises an epoxy resin and a polysulfide.

Other embodiments of the invention include substrates coated accordingto the above methods.

BROAD STATEMENT OF THE INVENTION

The present invention is addressed to thermally-protective, intumescentcoating systems and methods therefor which provide coatings havingoutstanding fire protection properties at minimal film thicknesses ofless than 1.27 cm (50 mils). Advantageously, such coatings are able towithstand typical sea exposure with no apparent loss in heat barrierproperties, exhibit a strong adherence to hull materials, and arecoatable with marine antifouling paint.

In this regard, it has been discovered that, owing to the severe thermaland convective environment developed during fire conditions, thereexists a critical region for obtaining toughness, stability, andprevention of char breakthrough of an intumescent coating or paint. By"breakthrough," it is meant the point at which the char or char foamformed from the decomposition of the coating layer is broken, separated,or otherwise affected by the fire to expose the substrate directly tothe flame environment. Breakthrough is usually not caused by the heat ofthe flame of the fire itself but by the flame environment where highshear forces are present that can erode or remove the intumescentcoating or paint. The present invention therefore involves providing thecoating as having a first component which forms a rigid carbonific charfoam having superior toughness and rigidity, and a second componentwhich forms an insulative carbonific char foam having a density abouthalf of the density of the rigid carbonific foam to give superiorinsulation properties. In providing two foam components, one protectingthe substrate from breakthrough and direct exposure to the flameenvironment, and the other insulating the substrate to protect it fromconductive, radiant, and/or convective heating by the flame environment,the present invention affords a capability to offer superior fireprotection at film thicknesses of less than 1.27 mm (50 mils).

It will be appreciated that the two foam components may be separatelyprovided in a laminate-type arrangement as, respectively, an innercoating layer coated and cured on a surface of the substrate to form aninner film layer, and an outer coating layer coated and cured on theinner film layer to form an outer film layer. It is preferred that theinner film layer is selected as intumescently decomposing to form therigid char foam component having superior toughness and rigidity, withthe outer film layer selected to form the insulative char foam componenthaving superior insulation properties. With such an arrangement, theinner film layer is made to remain intact until the outer film layerintumescently decomposes into the insulative char foam, which foaminsulates the substrate from the heat of the flame environment, butwhich may be eventually broken or otherwise degraded by the aggressivenature of the same. However, at the locations whereat the outerinsulative char foam layer has broken through to expose the inner filmlayer directly to the flame environment, the inner film layeradvantageously then decomposes to form the rigid char foam whichprotects the substrate from direct expose to the flame environment andthereby provides an additional degree of fire protection.

Alternatively, the two foams may be provided as being formed fromcomponents blended to comprise a single coating layer which is coatedand cured on the surface of the substrate to form a film layer. Forforming the rigid char foam, a first component is provided in thecoating layer which component is curable to form a first portion of thefilm layer which portion is thermally decomposable to form a char whichintumesces to form the rigid char foam. For forming the insulative charfoam, a second component is provided in the coating layer whichcomponent is curable to form a second portion of the film layer whichportion is blended with the first portion. The second portion of thefilm layer is thermally decomposable to form a char which charintumesces to form the insulative char foam which foam is blended withthe rigid char foam. Again, the rigid char foam component protects thesubstrate from breakthrough and the direct exposure to the flameenvironment, with the insulative char foam component protecting thesubstrate from conductive, radiant, and/or convective heating by theflame environment.

It is, therefore, an aspect of the present invention to provide acoating system for thermally protecting a substrate having a surfaceexposed to a flame environment. The coating system involves a firstcoating layer coated on the surface of the substrate and cured thereonto form a first film layer which layer is thermally decomposable uponexposure to the flame environment to form a first carbonific char whichchar intumesces to form a rigid carbonific char foam. A second coatinglayer is coated on the first film layer and cured thereon to form asecond film layer which layer is thermally decomposable upon exposure tothe flame environment to form a second carbonific char which charintumesces to form an insulative carbonific char foam having a densityabout half the density of the rigid carbonific char foam.Advantageously, the rigid carbonific char foam is made to form where theinsulative carbonific char foam has broken through to expose the firstfilm layer to the flame environment.

Another aspect of the present invention is to provide a method forthermally protecting a substrate having a surface exposed to a flameenvironment. The method involves the steps of coating the surface of thesubstrate with a first coating Layer, and then curing the first coatinglayer thereon to form a first film layer which layer is thermallydecomposable upon exposure to the flame environment to form a firstcarbonific char which char intumesces to form a rigid carbonific charfoam. A second coating layer is coated on the first film layer, and thenis cured thereon to form a second film layer which layer is thermallydecomposable upon exposure to the flame environment to form a secondcarbonific char which char intumesces to form an insulative carbonificchar foam having a density about half the density height of the rigidcarbonific char foam. Advantageously, the rigid carbonific char foam ismade to form where the insulative carbonific char foam has brokenthrough to expose the first film layer to the flame environment.

Yet another aspect of the present invention is a coating composition forthermally protecting a substrate having a surface exposed to a flameenvironment on which the composition is coated and cured to form a filmlayer. The composition is formulated from a blend of a first and asecond component. The first component is curable to form a first portionof the film layer, the first portion being thermally decomposable toform a first carbonific char which char intumesces to form a rigidcarbonific char foam. The second component is curable to form a secondportion of the film layer which portion is blended with the firstportion. The second portion is thermally decomposable to form a secondcarbonific char which char intumesces to form an insulative carbonificchar foam blended with the rigid carbonific char and having a densityabout half the density of the rigid carbonific char foam.

Still another aspect of the present invention is the provision of amethod for thermally protecting a substrate having a surface exposed toa flame environment. The method involves the step of coating the surfaceof the substrate with a coating layer formulated from a blend of a firstcomponent and a second component. The first component is curable to forma first portion of a film layer, which portion is thermally decomposableto form a first carbonific char which char intumesces to form a rigidcarbonific char foam. The second component is curable to form a secondportion of the film layer which portion is blended with the firstportion and is thermally decomposable to form a second carbonific charwhich intumesces to form an insulative carbonific char foam blended withthe rigid carbonific char. The insulative char foam is provided to havea density of about half the density of the rigid carbonific char foam.The coating layer is cured on the surface of the substrate to form thefilm layer.

An advantage of the present invention includes a thermally-protective,intumescent coating system having improved insulation properties atminimal film thickness of about 1.27 mm (50 mils), and which is suitablefor marine and other applications. Another advantage is the ability toprovide laminar coating composition optimizing the fire protectionproperties of each of the lamina. These and other advantages will bereadily apparent to those skilled in the art based upon the disclosurecontained herein.

DETAILED DESCRIPTION OF THE INVENTION

The intumescent coating system and method of the present invention isprovided as having a first component which is curable to form a filmlayer, and a second component which also is curable to form a filmlayer. By "curable," it is meant that the first and second componentseach polymerizes, cross-links, vulcanizes, or otherwise reacts to form athermoplastic or thermosetting polymeric structure. In accordance withthe precepts of the invention, the first and second component may beapplied to a substrate in a laminate-type arrangement as, respectively,an inner coating layer coated and cured on a surface of the substrate toform an inner film layer, and an outer coating layer coated and cured onthe inner film layer to form an outer film layer. Alternatively, the twocomponents may be provided as blend which blend comprises a singlecoating layer which is coated and cured on the surface of the substrateto form a film layer. In either arrangement, the first component isselected as forming a film layer or a portion thereof which thermallydecomposes upon exposure to a flame environment to form a carbonificchar which intumesces to form a rigid carbonific char foam which iseffective to protect the substrate from breakthrough and direct exposureto the flame environment. The second component is selected relative tothe first component as forming a film layer or a portion thereof whichthermally decomposes upon exposure to a flame environment to form acarbonific char which intumesces to form an insulative carbonific charfoam which is effective to insulate the substrate and protect it fromconductive, radiant, and/or convective heat transfer from the flameenvironment.

When employed in a laminate-type arrangement, it has been observed thatthe inner film layer formed from the curing of the first component isprovided to remain intact until the outer film layer formed from thecuring of the second component intumescently decomposes into aninsulative char foam. Although the insulative char foam insulates thesubstrate from the heat of the flame environment, it is necessarilyprovided as having an open cellular morphology which may be eventuallybroken or otherwise degraded by the aggressive nature of the flames. Inthis regard, however, the inner and outer layers functionsynergistically in that at the locations where the outer insulative charfoam layer has broken through to expose the inner film layer directly tothe flame environment, the inner film layer advantageously thendecomposes to form the rigid char foam which protects the substrate fromdirect expose to the flame environment and thereby provides anadditional degree of fire protection. Alternatively, when the first andsecond components of the invention are applied as a blended layer, whichlayer thermally decomposes and intumesces to form a foam blend, theinsulative char foam portion of the foam blend again is seen asprotecting the substrate from damage from conductive, radiant, and/orconvective heat transfer from the flame environment. Likewise, the rigidchar foam portion of the foam blend again is seen as being effective tostrengthen the foam blend and to thereby protect the substrate from thedirect exposure to the flame environment which would attend anybreakthrough of the foam.

As to the physical properties which the foams of the first and secondcomponent of the invention are selected to exhibit, it is preferred thatthe cured film of the first component intumesces into a rigid or hardcarbonific char foam having a density about twice that of the insulativeor soft carbonific char foam of the cured film of the second component.In this regard it will be appreciated that, as heat conduction through agas can be several orders of magnitude lower than through a solid, thelower density foam of the second component will exhibit a thermalconductivity correspondingly lower than that of the higher density foamof the first component. However, as the foam of the cured film of thefirst component is twice as dense, it will be correspondingly stronger,harder, and more rigid than the necessarily softer foam of the curedfilm of the second component.

Quantitatively, in one aspect of the invention it is preferred that therigid carbonific char foam of the first component is selected as havinga density of between about 0.5 g/cm³ and less than about 1.0 g/cm³, withthe insulative carbonific char foam being selected as having a densityof between greater than about 0.01 g/cm³ and less than about 0.5 g/cm³.In another aspect of the invention, the rigid foam also will be seen ashaving a foam expansion height about half the expansion height of theinsulative foam. In this regard, a 0.25 mm (10 mil) thick layer of thecured film of the first component has been observed to intumesce into afoam having an expansion height of 2.54 cm (1 inch), while a 0.254 mm(10 mil) thick layer of the cured film of the second component has beenobserved to intumesce into a foam having an expansion height of 5.08 cm(2 inches). As measured by ASTMD 1415-56T, the rigid foam of the firstcomponent is correspondingly harder as having a penetration depth ofonly 0.3 mm (11.8 mil) as compared to the relatively softer foam of thesecond component having a penetration depth of 0.7 mm (27.6 mil).

Considering the preferred formulation of the second component, the curedfilm thereof which thermally decomposes and intumesces into theinsulative carbonific char foam component of the present invention, thecomponent is formulated as comprising a combination of ingredients whichare curable but reactive upon subsequent thermal exposure to form anincombustible residue which is expandable to a carbonific cellular foam.These ingredients, however, are selected to melt, react or decompose ina particular sequence to develop a desired viscosity profile, as well asa desired time-temperature history which is the sum of the exothermic orendothermic reactions occurring inside the coating, and of the net heattransfer into and out of the intumescing coating. Broadly, the secondcomponent of the present invention comprises a polymeric binder orvehicle, a char promoter, a dehydrating agent, a spumific or blowingagent, and optionally, pigments and solvents.

Preferably, the binder or vehicle for carrying the intumescentingredient mixture is curable and comprises an epoxy-polysulfide systemor, alternatively, an epoxy-chlorosulfonated polyethylene system, anaminoplastic system such as urea-melamine-formaldehyde, or a siloxanepolymer such as a polysiloxane, a polysilarylene, or a derivativethereof, such as, for example, Siloxirane™ 2433 manufactured by AdvancedPolymer Sciences, Inc., of Avon, Ohio. If an epoxy-based binder systemis employed, the catalyst for the epoxy resin, preferably a polysulfide,polyamine, polyamide, or the like, may be provided as a B-stagecomponent for addition to the A-stage resin prior to application. As thename suggests, the binder, typically in conjunction with a solvent, wetsand holds together the ingredients in the coating formulation. Beforecure, the binder provides for homogeneous film-forming. After cure, thebinder imparts mechanical integrity to make the coating durable. Thebinder also assists in sealing the char for improved foaming and cancontribute to the amount of char developed.

The char developed in the intumescent coating formulation of the presentinvention is formed by the acid-catalyzed dehydration of a polyhydricchar promoter to yield a carbon char and water. For purposes of theformulation of the present invention, the polyhydric substance is apolyol, with pentaerythritol, dipentaerythritol, and derivatives andmixtures thereof being preferred. Alternatively, other char promoters,such as sugars, polyhydric phenols, or starches, may be substituted.

The polyhydric char promoter of the subject formulation is selected tocontain hydroxyl functional groups which are subject to a dehydrationreaction. Accordingly, a dehydrating agent, preferably an acid or anacid precursor such as an ammonium polyphosphate, a magnesium phosphate,a phosphite, or an organophosphate ester which is thermally decomposableto form an acid catalyst such as phosphoric acid, is included todehydrate the char promoter to form water and an intermediate speciessuch as an ester. Advantageously, the intermediate species is readilythermally decomposable to form a relatively incombustible carbonificchar which may be made somewhat self-extinguishing via the liberation ofcarbon dioxide during the dehydration. Moreover, the latent heat ofevaporation of the water condensed by the dehydration of the charpromoter endothermically contributes to the insulative effects of thecoating formulation.

The char developed during the acid-catalyzed dehydration of the charpromoter is expanded into a carbonific char foam having a relatively lowthermal conductivity which, together with the endothermic decompositionand dehydration reactions, effects the insulative efficiency of thecoating. To expand the char, a blowing agent or spumific is employed forits decomposition at a desired temperature and attendant liberation of anonflammable gas such as nitrogen. For purposes of the presentinvention, a blowing agent such as dicyandiamide or an azodicarbonamideis preferred, although another blowing agent such as a melamine, aguanidine, a glycine, a urea, or an organohalophosphate esterderivative, or a chlorinated or halogenated organic material such as achlorinated paraffin, may be substituted. Of utmost importance to theformation of a thick, uniform foam, however, is that the blowing agentdecomposes at a temperature higher than the decomposition temperaturesof both the intermediate species and the dehydrating agent.

As to optional additives, the toughness of the carbon foam may beimproved through the use of thermally-stable aminoplast resins such asurea-melamine-formaldehyde resins which form a tough matrix for thecellular mass. Similarly, glass-forming materials such as berates,silicates, mica, glass fibers and the like optionally may be added asinert, char-reinforcing agents. A zinc oxide additive may be employed toreduce the amount of smoke generated during the intumescent reaction.Additionally, the viscosity of the formulation may be thinned with asolvent such as methyl ethyl ketone, methyl isobutyl ketone, a naphtha,or a mixture thereof to facilitate spray application.

Considering now the preferred formulation of the first component, suchformulation may be functionally characterized as curable to form a filmwhich film thermally decomposes and intumesces into the hard or rigidcarbonific char of the present invention selected as having a structuralintegrity sufficient to withstand the turbulent convective currentsgenerated in an active fire or flame environment. In this regard, acoating marked under the name FIREX™ by the Pfizer Co. of New York,N.Y., has been found to meet the necessary functional requirements. Thecomposition of the FIREX™ brand coating may be broadly described as atwo-part, epoxy resin system comprising a first component of a filledpolysulfide polymer and a second component of a filled liquid epoxyresin.

Advantageously, the coating method and system of the present invention,wherein a first component is provided to form a hard, rigid foam and asecond component is provided for forming a soft, insulative foam, may beadapted for a variety of applications. For example, depending upon theapplication contemplated and whether insulation value or coating weightis the overwhelming consideration, the practitioner may utilize twocoating layers of the second component over a primer coat layer of thefirst component. A topcoat of the first component also may be employedover the second component coating layers. In such an arrangement, it hasbeen observed that the topcoat layer, the cured film of which forms ahard or rigid char foam, protects the developing foam of the innerlayers of the second component from breakthrough. In this way, theinsulation and char stability of each layer in the coating laminate isoptimized to achieve improved fire protection capabilities.Additionally, and as aforementioned, the first and second components ofthe present invention may be provided in a blended form. Such a blend isattractive in that acceptable fire protection may be achieved with fewercoats and, accordingly, a reduced overall coating thickness.

As the experimental data will show, the bi-component coating system ofthe present invention provides superior fire protection as compared to asingle component coating when applied to, for example, marine hullmaterials such as DURA. DURA is an advanced special hull treatmentmaterial, proprietary to the U.S. Navy, which is described in TheJournal of the Acoustical Society of America, Vol. 77, No. 3, pp.1229-1238 (1985), to comprise a polyurethane formed from a toluenediisocyanate and a polytetramethylene glycol. Indeed, in addition toproviding superior fire protection, the components of the coating systemof the invention have been found to adhere strongly to marine hullmaterials such as DURA and the like, to be coatable with antifoulingpaint, and to be capable of withstanding typical sea exposure with noapparent loss in insulative properties.

Additionally, the coating system of the present invention will findapplication in the general fire protection of homes, commercialbuildings, and the like. In this regard, the inventive system may beapplied as a coating to ceiling tiles which typically are supported witha metal grid, tray, or runner assembly, or with a tongue-in-groove,interlocking arrangement. During fires, it has been observed that thefibrous material from which the ceiling tiles are formed undergoes adegree of shrinkage, which shrinkage loosens the tiles and results intheir falling from the ceiling. The expansion of the coating system ofthe invention, however, accommodates for the shrinkage of the tiles. Thetiles therefore are made to remain secure in their support to lessen thechances that an occupant of the home or building will be struck by afalling tile. For such applications, it has been found that apolysiloxane or a derivative thereof is preferred for the bindercomponent of the system as promoting a better adhesion with ceiling tilematerials.

The examples to follow are illustrative of the precepts of the presentinvention but should not be construed in a limiting sense. Allpercentages and proportions are by weight, unless otherwise expresslyindicated.

EXAMPLES

A pilot plant batch of an intumescent coating composition, Formula No.45852-232, the cured film of which forms an insulative char foamaccording to the precepts of the present invention, was prepared as atwo-part system having a weight per gallon of 10.982 lbs. (6.358 kg/l),a total solids content of 76%, and a composition as follows:

                  TABLE 1                                                         ______________________________________                                        Ingredients   Description  Weight-% Volume-%                                  ______________________________________                                        Component A                                                                   Dipentaerythritol                                                                           char promoter                                                                              13.56    13.14                                     Ammonium Polyphosphate.sup.1                                                                dehydrating agent                                                                          27.13    19.96                                     Azodicarbonamide.sup.2                                                                      spumific     1.74     1.39                                      Polysulfide.sup.3                                                                           binder       12.74    13.22                                     Epoxy Resin.sup.4                                                                           binder       12.74    9.70                                      Magnesium phosphate                                                                         acid catalyst                                                                              7.05     4.23                                      Black Iron Oxide                                                                            pigment      0.54     0.15                                      Methyl Isobutyl Ketone                                                                      solvent      9.65     15.86                                     High Flash Naphtha                                                                          solvent      14.48    21.87                                     Total Component A          99.63    99.52                                     Component B                                                                   Primary Amine epoxy resin catalyst                                                                       0.37     0.48                                      Total Component B          0.37     0.48                                      ______________________________________                                         .sup.1 PHOSCHECK P30 ™ (Monsanto, St. Louis, MO)                           .sup.2 CELOGEN AZ ™ (Uniroyal, Middleberg, CN)                             .sup.3 THIOKOL LP3 ™ (Morton International, Chicago, IL)                   .sup.4 EpIREZ 5183 ™ (Rohne Poulene, Louisville, KY)                       .sup.5 EH330 ™ (Morton International, Chicago, IL)                    

Prior to the addition of the component B catalyst, component A was mixedthoroughly with a power mixer and was shaken for 30 minutes. Thecomponent B catalyst then was added to the thoroughly mixed Component Aat a weight ratio (A/B) of 100/0.37. To facilitate the addition, themixed Component A was placed under slow agitation using a power mixerwith Component B being slowly added. The agitation was continued for 5minutes. The pot life of the catalyzed mixer was found to be about 8-10hours depending upon the ambient temperature.

Example 1

To validate the precepts of the present invention, the No. 232formulation prepared above was used as a coating layer in combinationwith the commercial FIREX™ formulation selected as thermally decomposingto form the hard or rigid carbonific char of the present invention. Inthis regard, DURA panels were coated with various layers of the No. 232and FIREX™ formulations, with a single FIREX™ layer coating being usedas a control. The compositions of the coating layers employed were asfollows:

                  TABLE 2                                                         ______________________________________                                        Coating Layer                                                                              Composition     Weight-%                                         ______________________________________                                        FIREX ™   Component A.sup.1                                                                             57.0                                                          Component B.sup.2                                                                             43.0                                             Formula No. 232                                                                            Component A     99.63                                                         Component B     0.37                                             Topcoat Blend                                                                              FIREX ™ (as above)                                                                         75.00                                                         Formula No. 232 (as above)                                                                    25.00                                            ______________________________________                                    

Each of the DURA test panels was power buffed with a disc sander using40-grit paper. The resulting appearance was a smooth, dull gray finish.To the sanded DURA panels were applied various layers of the coatingcompositions of Table 2. All coatings were applied using a WAGNER™ HeavyDuty Power Painter airless sprayer equipped with a 0.6-mm nozzle.Samples were coated as listed in Table 3 according to the coating andcure schedule described in Table 4.

                  TABLE 3                                                         ______________________________________                                        Coating Layer    Dry Film Thickness, mm (mils)                                Sample No. →                                                                            61      61-1    61-2  61-3                                   ______________________________________                                                         Control                                                      FIREX ™ primer (70% in MEK).sup.1                                                           1.27    0.366   0.284 0.287                                                   (50)    (14.4)  (11.2)                                                                              (11.3)                                 Formula No. 232 (1st coat).sup.2                                                                       0.257   0.231 0.226                                                           (10.1)   (9.1)                                                                               (8.9)                                 Formula No. 232 (2nd coat).sup.2                                                                       0.300   0.314 0.328                                                           (11.4)  (12.4)                                                                              (12.9)                                 FIREX ™ topcoat (67% in MEK).sup.3                                                                          0.386                                                                         (15.2)                                       FIREX ™ /No. 232 blend (75/25).sup.4                                                                              0.229                                                                          (9.0)                                 Total Dry Film Thickness                                                                       1.27    0.912   1.22  1.07                                                    (50)    (35.9)  (47.9)                                                                              (42.1)                                 ______________________________________                                         .sup.1 Material received at 80% and thinned for spraying by addition of       10% methyl ethyl ketone by weight.                                            .sup.2 74% solids as manufactured                                             .sup.3 Material received at 80% solids and thinned for spraying by            addition of 14% methyl ethyl ketone by weight to achieve a uniform, wet       coating. Although the material sprayed easily and exhibited the desired       wet film properties, some solvent popping was observed which resulted in      an occasional small pinhole. Accordingly, slightly less solvent, e.g.,        8-10%, is indicated.                                                          .sup.4 FIRE ™ received at 80% solids and thinned for spraying by           addition of 13% methyl ethyl ketone. Formula No. 232, 74% solids as           manufactured, was blended with the FIREX ™ (75/25 FIREX/No. 232 by         weight).                                                                 

                  TABLE 4                                                         ______________________________________                                        Day      Preparation                                                          ______________________________________                                        1        Apply FIREX ™ primer (all Samples);                                        Retain panels in spray area for 4 hours;                                      Place panels in controlled environment (75° F., well                   ventilated); and                                                              Age panels 24 hours.                                                 2        Apply 1st coat Formula No. 232 (Samples 61-1,                                 61-2, 61-3);                                                                  Retain panels in spray area for 4 hours;                                      Place panels in controlled environment (75° F., well                   ventilated); and                                                              Age panels 72 hours..sup.1                                           5        Apply 2nd coat Formula No. 232 (Samples 61-1,                                 61-2, 61-3);                                                                  Retain panels in spray area for 4 hours;                                      Place panels in controlled environment (75° F., well                   ventilated); and                                                              Age panels 48 hours..sup.1                                           7        Apply topcoats according to Table 3 (Samples 61-2,                            61-3);                                                                        Retain panels in spray area for 4 hours; and                                  Place panels in controlled environment (75° F., well                   ventilated).                                                         9        Remove panels for adhesion testing.                                  ______________________________________                                         .sup.1 Although aging times of 48 and 72 hours are noted, and while longe     aging times are acceptable provided intercoat adhesion is attained, it ha     been demonstrated that an aging time of 24 hours at 75° F. and les     than 50% Relative Humidity is sufficient.                                

In summary, no unexpected or unusual conditions were encountered in thepreparation of the test panels. All films were applied as wet coatings,and the cured films exhibited a good appearance.

The adhesion of each coat applied to each of the DURA panels wasevaluated using a tape pull as specified in A.S.T.M. 3359. The resultswere as follows:

                  TABLE 5                                                         ______________________________________                                                         Sample No.                                                   Coating Layer      61-1      61-2   61-3                                      ______________________________________                                        FIREX ™ primer  5A        5A     5A                                        (Adhesion after 24 hours).sup.1                                               Formula No. 232 (1st coat)                                                                       4A        4A     4A                                        (Adhesion after 72 hours).sup.1                                               Formula No. 2.32 (2nd coat)                                                                      5A        5A     5A                                        (Adhesion after 48 hours).sup.1                                               FIREX ™ topcoat.sup.1     5A                                               FIREX ™/No. 232 blend (75/25)    5A                                        (Adhesion after 48 hours).sup.1                                               ______________________________________                                         .sup.1 Adhesion evaluated by tape pull procedure specified in A.S.T.M.        3359. Ratings of 4A and 5A are considered to be excellent.               

In summary, the intercoat adhesion between each coat in the coatings, aswell as the overall adhesion of the entire coating laminate, was foundto be excellent.

Example 2

To validate the fire protection afforded according to the precepts ofthe present invention, the thermal responses of the coating systemsdescribed in Table 3 were evaluated as measured by the fire resistanceof the substrate. The DURA test panels (30 cm by 30 cm, 12 inch by 12inch) prepared in accordance with the coating protocol set forth inTables 3 and 4, were quartered for burn testing, as was the controlspecimen, Sample No. 61, which was prepared as having only a singleFIREX™ coating layer of a dry film thickness of 1.27 mm (50 mils).

The burn testing was conducted using a small scale fire test apparatus.The apparatus consisted of a Fisher burner (Model No. 03-900) having a2.5 cm (1 inch) diameter diffuser cap (Model No. 03-900-10). The burnerwas operated with its air vents fully opened, and the gas input rate wasadjusted to generate a 0.3175 cm (1/8 inch) high flame cone immediatelyabove the cap of the burner.

Each of the 10.2 cm by 10.2 cm (4-inch by 4-inch) test specimens wascentered above the burner at a 45° angle and at a nominal distance of6.35 cm (2.5 inches) from the center of the specimen to the top of theburner. The burner then was adjusted to achieve the 0.3175 cm (1/8 inch)flame cone which was maintained under the specimen for 15 to 20 minutes.The essentially convective heat flux into the specimen was estimated at3.51×10³ kJ/hr/m² (30,000 Btu/hr/ft²). The following results wereobserved:

                  TABLE 6                                                         ______________________________________                                                  Time Over Flame                                                     Sample No.                                                                              (minutes:seconds)                                                                           Observation                                           ______________________________________                                        61-1.sup.1                                                                               3:30         Char fully expanded and                                                       edges are separated away                                                      from FIREX ™ primer.                                          3:35         FIREX ™ primer slightly                                                    visible around edges of                                                       char, but is not involved                                                     in fire or char. Primer                                                       appears slightly liquid.                                         3:40         Conditions stable, no                                                         flaming or dripping.                                            15:00         No change. Char bubble                                                        stable.                                                         60:00         No change. Test                                                               discontinued.                                         61-2.sup.2                                                                               1:00         Large 12.7 cm (5 inch)                                                        char bubbled formed.                                                          Minor surface flaming for                                                     30 seconds.                                                      2:00         Char bubble stable.                                             15:00         Char bubble stable.                                             60:00         Char bubble stable. No                                                        smoking or dripping.                                                          Entire panel surface                                                          intact. Test                                                                  discontinued.                                         61-3.sup.3                                                                               1:00         Some surface flaming.                                                         Small bubble formed                                                           (about half the size of                                                       bubble formed in Sample                                                       No. 61-2).                                                       2:00         Char bubble stable; flame                                                     extinguished.                                                   10:00         Coating expanded away                                                         from sample at edges                                                          where sample was                                                              quartered. Some dripping                                                      from bottom edge cut.                                           12:00         Dripping stopped.                                               22:00         Smoking from separation                                                       on both side edges.                                                           Center char bubble                                                            intact.                                                         35:00         Some smoking but no                                                           dripping. Center char                                                         bubble is stable.                                               60:00         No. change. Entire                                                            surface panel intact.                                                         Test discontinued.                                    61.sup.4   5:00         Major cracks in center of                                                     char bubble.                                                     5:37         Some flaming from center                                                      cracks.                                                          9:00         Cracks opening around                                                         bottom perimeter of char                                                      bubble and some flaming.                                                      Center cracks "healed";                                                       no flaming.                                                     11:00         Flaming around char                                                           perimeter, but DURA not                                                       yet ignited.                                                    13:30         Smoking and passive                                                           flames continue.                                                16:20         Char bubble breaks open.                                        17:40         Active burning.                                                 19:10         DURA involved in fire,                                                        major dripping.                                                 20:30         DURA flaming; test                                                            discontinued.                                         ______________________________________                                         .sup.1 FIREX ™ primer, 2 coats No. 232, no topcoat                         .sup.2 FIREX ™ primer, 2 coats No. 232, FIREX ™ topcoat                 .sup.3 FIREX ™ primer, 2 coats No. 232, FIREX ™/No. 232 (75/25)         blend topcoat                                                                 .sup.4 FIREX ™ control                                                

The burn test results confirm the precepts of the invention in thatoptimal fire protection is provided when a bi-component coating systemis employed to provide two foam components, one being relatively rigidand hard to protect the substrate from breakthrough and direct exposureto the flame environment, and the other being relatively soft andinsulative to protect the sustrate from conductive, radiant, and/orconvective heating by the flame environment. Although Sample No. 61-2(FIREX™ topcoat over 2 coats of Formula No. 232 and 1 coat of FIREX™primer) qualitatively appears to be preferred in maintaining the mostintegrity overall, i.e., even after 60 minutes there was no breaking inthe coating surface, Sample No. 61-1 (2 coats of Formula No. 232 over 1coat of FIREX™ primer) nevertheless provides fire performance improvedover that attainable with the conventional intumescent coating of SampleNo. 61 (FIREX™ control). Sample No. 6-3 (FIREX™/No. 232 blend topcoatover 2 coats of Formula No. 232 and 1 coat of FIREX™ primer) alsoexhibits improved fire protection and thereby validates another aspectof the invention.

Example 3

The fire protection afforded according to the precepts of the presentinvention was again validated using a second burn test proceduredesigned to more approximate the effects of an aggressive, large-scalefire. This procedure entailed igniting a 0.61 m by 0.61 m (2 ft by 2 ft)pan of heptane beneath a specimen held at a 45° angle to the pan. Thethermal responses of 0.9 m by 0.91 m (3 ft by 3 ft) DURA samplesprepared in accordance with Tables 3 and 4 were compared with that of acontrol specimen coated with a 1.27 mm (50 mil) FIREX™ layer. Theessentially radiative heat flux into the specimen was estimated to be1.76×10³ kJ/hr/m² (15,000 Btu/hr/ft²). The fire resistance afforded bythe coatings was noted as the time in minutes to the ignition of thesubstrate, with the following results having been observed:

                  TABLE 7                                                         ______________________________________                                                     Sample No.                                                       Composition    61-1   61-2     61-3 61 (Control)                              ______________________________________                                        FIREX ™ primer                                                                            X      X        X                                              Formula No. 232 (1st coat)                                                                   X      X        X                                              Formula No. 232 (2nd coat)                                                                   X      X        X                                              FIREX ™ topcoat    X                                                       FIREX ™/No. 232             X                                              (75/25) blend topcoat                                                         FIREX ™ Control                                                            (1.27 mm)                           X                                         (50 mil)                                                                      Fire Resistance                                                               (min:sec to failure)                                                                         17:40  >24.sup.1                                                                              16:23                                                                              7:35                                      ______________________________________                                         .sup.1 The pan of heptane supported burning for approximately 8 minutes,      but would extinguish and have to be replaced. After 3 pans of heptane, th     fire resistance of Sample No. 612 was recorded as >24 minutes. However, a     the char of Sample No. 612 was observed still to be in excellent              condition, it undoubtedly would have been stable for considerably longer      than 24 minutes.                                                         

These data corroborate the validity of the precepts of the invention inthat optimal fire protection again is observed to be provided when abi-component coating system is employed to provide a rigid or hard foamcomponent to protect the substrate from breakthrough and direct exposureto the flame environment, in conjunction with a soft or insulative foamcomponent to protect the substrate from conductive, radiant, and/orconvective heating by the flame environment. Again, although Sample No.61-2 (FIREX™ topcoat over 2 coats of Formula No. 232 and 1 coat ofFIREX™ primer) qualitatively appears to be preferred in maintaining themost integrity overall, Sample No. 61-1 (2 coats of Formula No. 232 over1 coat of FIREX™ primer) nevertheless provides fire performance improvedover that attainable with the conventional intumescent coating of SampleNo. 61 (FIREX™ control). Sample No. 6-3 (FIREX™/No. 232 blend topcoatover 2 coats of Formula No. 232 and 1 coat of FIREX™ primer) alsoexhibits improved fire protection and thereby again validates anotheraspect of the invention.

Example 4

Example 4 discloses a fire-resistant ceiling tile where a conventionalor acoustical ceiling tile is coated with an intumescent coating asdescribed below that obtained a dry film thickness of 0.86-0.97 mm(34-38 mils) which had 118-120 g dry coating weight per 0.12 m² (perft²) and yielded over a sixfold improvement in fire resistance. Thefire-retardant intumescent coating was formulated as described in Table1, except that the black iron oxide pigment was replaced with an equalamount by weight of a pigment that was a 50/50 mixture of TiO₂ and Al₂O₃.3H₂ O. The resultant coating was applied to the tile by airless sprayin a 50% overlap crosscoat pattern to obtain a dry film thickness of0.91±0.05 mm (36±2 mils). Fire resistance was measured by securing a30.5 cm×30.5 cm (1×1 foot) sample of coated tile approximately 5.08 cm(2 inches) above a Fisher Burner calibrated at 1.76×10³ kJ/hr/m² (18,000BTU/hr/ft²). Results were as follows:

                  TABLE 8                                                         ______________________________________                                        Fire Resistance of Coated Tiles                                               Material       Tile (minutes to ignition)                                     ______________________________________                                        Uncoated Tile    10                                                           Coated Tile coating                                                                          >60*                                                           0.91 (36 mils) dry                                                            ______________________________________                                         *Test was discontinued after 60 minutes.                                 

Example 5

Example 5 discloses a fire-resistant drywall paper and board where aconventional drywall paper and board were coated with an intumescentpaint as described below where a dry film thickness of 0.30-0.38 mm(12-15 mils) yielded a twentyfold increase in fire resistance.

A fire-retardant intumescent coating for Kraft paper (facing forstandard dry wall construction board) was formulated as in Example 4.The coating was applied to Kraft paper (unsupported) and to Kraftpaper-covered wall board by airless spray in the same manner as inExample 4 to obtain a 0.30-0.38 mm dry (12-15 mils dry) fire-retardantintumescent coating. Adhesion to the paper in both situations wasexcellent.

Fire resistance was evaluated as described in Example 4, above. Resultswere as follows:

                  TABLE 9                                                         ______________________________________                                        Fire Resistance of Coated Paper and Wall Board                                Material             Time (minutes to ignition)                               ______________________________________                                        Standard Dry Wall Sheet                                                                            <30       seconds                                        (faced with Kraft paper)                                                      Kraft paper (uncoated)                                                                             <30       seconds                                        Kraft paper - coated, 0.30-0.38 mm,                                                                10        minutes                                        dry (12-15 mils))                                                             ______________________________________                                    

The data for Examples 4 and 5 demonstrate excellent fire protection fora one layer system. Even better protection will be obtained by use ofthe multilayer system disclosed herein. An example would be coating thesurface of a substrate (e.g.: conventional or acoustical ceiling tile,drywall paper and board, Kraft paper, wood, and the like) with a firstcoating layer cured thereon to form a first film layer which layer isthermally decomposable upon exposure to fire conditions to form a firstcarbonific char which char intumesces to form a first rigid carbonificchar foam; and a second coating layer coated on the first film layer andcured thereon to form a second film layer which layer is thermallydecomposable upon exposure to fire conditions to form a secondcarbonific char which char intumesces to form an insulative carbonificchar foam having a density about half the density of the first rigidcarbonific char foam, the first rigid carbonific char foam forming wherethe insulative carbonific char foam has broken through to expose thefirst film layer to fire conditions.

While the forms of the invention herein disclosed constitute presentlypreferred embodiments, many others are possible. It is not intendedherein to mention all of the possible equivalent forms or ramificationsof the invention. It is to be understood that the terms used herein aremerely descriptive, rather than limiting, and that various changes maybe made without departing from the spirit of the scope of the invention.

What is claimed:
 1. An intumescent coating system for thermallyprotecting a substrate having a surface exposed to fire conditionscomprising:(a) a first coating layer coated on the surface of saidsubstrate and cured thereon to form a first film layer which layer isthermally decomposable upon exposure to said fire conditions to form afirst carbonific char which char intumesces to form a first rigidcarbonific char foam; and (b) a second coating layer coated on saidfirst film layer and cured thereon to form a second film layer whichlayer is thermally decomposable upon exposure to said fire conditions toform a second carbonific char which char intumesces to form aninsulative carbonific char foam; and wherein said intumescent coatingsystem has a thickness of 1.27 mm (50 mils) or less.
 2. The intumescentcoating system of claim 1 wherein said insulative carbonific char foamhas a density of between about 0.01 g/cm³ and less than about 0.5 g/cm³.3. The intumescent coating system of claim 1 wherein upon exposure tofire conditionssaid rigid carbonific char foam is harder relative tosaid insulative carbonific char foam.
 4. The intumescent coating systemof claim 1 wherein, upon exposure to fire conditions, said insulativecarbonific char foam comprises a lower density foam exhibiting has alower thermal conductivity relative to said rigid carbonific char foam.5. The intumescent coating system of claim 1 further comprising a thirdcoating layer coated on said second film layer and cured thereon to forma third film layer which layer is thermally decomposable upon exposureto said fire conditions to form a third carbonific char which charintumesces to form a second rigid carbonific char foam, said insulativecarbonific char foam forming under said second rigid carbonific charfoam.
 6. The intumescent coating system of claim 1 further comprising athird coating layer formulated as a blend of said first and said secondcoating layers, said third coating layer being coated on said secondfilm layer and cured thereon to form a third film layer which layer isthermally decomposable upon exposure to said fire conditions to form athird carbonific char which char intumesces to form a carbonific charfoam blend, said insulative carbonific char foam forming under saidcarbonific char foam blend.
 7. A method for thermally protecting asubstrate having a surface exposed to fire conditions comprising thesteps of:(a) coating said surface of said substrate with a first coatinglayer; (b) curing said first coating layer on said surface of saidsubstrate to form a first film layer which layer is thermallydecomposable upon exposure to said fire conditions to form a firstcarbonific char which char intumesces to form a first rigid carbonificchar foam; (c) coating a second coating layer on said first film layer;and (d) curing said second coating layer on said first coating layer toform a second film layer which layer is thermally decomposable uponexposure to said fire conditions to form a second carbonific char whichchar intumesces to form an insulative carbonific char foam; andwhereinsaid first and second film layers comprise an intumescent coating systemhaving a thickness of 1.27 mm (50 mils) or less.
 8. The method of claim7 wherein said insulative carbonific char foam has a density of betweenabout 0.01 g/cm³ and less than about 0.5 g/cm³.
 9. The method of claim 7wherein said rigid carbonific char foam has a density of between about0.5 g/cm³ and less than about 1.0 g/cm³, and said insulative carbonificchar foam has a density of between greater than about 0.01 g/cm³ andless than about 0.5 g/cm³.
 10. The method of claim 7 further comprisingthe steps of:(e) coating a third coating layer on said second filmlayer; and (f) curing said third coating layer on said second coatinglayer to form a third film layer which layer is thermally decomposableupon exposure to said fire conditions to form a third carbonific charwhich char intumesces to form a second rigid carbonific char foam, saidinsulative carbonific char foam forming under said second rigidcarbonific char foam.
 11. The method of claim 7 further comprising thesteps:(e) coating a third coating layer on said second film layer, saidthird coating layer formulated as a blend of said first and said secondcoating layers; and (f) curing said third coating layer on said secondcoating layer to form a third film layer which layer is thermallydecomposable upon exposure to said fire conditions to form a thirdcarbonific char which char intumesces to form a carbonific char foamblend having a first foam component, and a second foam component, saidinsulative carbonific char foam forming under said carbonific char foamblend.
 12. The substrate coated according to the method of claim
 7. 13.The substrate coated according to the method of claim
 10. 14. Thesubstrate coated according to the method of claim
 11. 15. Theintumescent coating system of claim 1 wherein said rigid carbonific charfoam has a density of between about 0.5 g/cm³ and less than about 1.0g/cm³, and said insulative carbonific char foam has a density of betweengreater than about 0.01 g/cm³ and less than about 0.5 g/cm³.
 16. Theintumescent coating system of claim 1 further comprising a third coatinglayer coated on said second film layer and cured thereon to form a thirdfilm layer which layer is thermally decomposable upon exposure to saidfire conditions to form a third carbonific char which char intumesces toform a second insulative carbonific char foam.
 17. The intumescentcoating system of claim 5 wherein said first and second rigid carbonificchar foams have a density of between about 0.5 g/cm³ and less than about1.0 g/cm³, and said insulative carbonific char foam has a density ofbetween greater than about 0.01 g/cm³ and less than about 0.5 g/cm³. 18.The method of claim 10 wherein said first and second rigid carbonificchar foams have a density of between about 0.5 g/cm³ and less than about1.0 g/cm³, and said insulative carbonific char foam has a density ofbetween greater than about 0.01 g/cm³ and less than about 0.5 g/cm³.